Redaction has a graveyard of famous failures: court filings, government reports and corporate documents where "blacked out" text was recovered by anyone who selected it and copied. The mistake is always the same.
A PDF page is layers: the text lives in one, your black rectangle in another. Cover text with a box and the text is still there — select-all, copy, paste into a text editor, and the secret is out. Even "print to PDF" sometimes preserves the text layer underneath.
Proper redaction rewrites the page so the sensitive content no longer exists in the file. Kameleo does this by rasterizing: every page you drew boxes on is re-rendered into a flat image with the boxes burned into the pixels. The text underneath isn't hidden — it's gone. Pages without boxes keep their text layer untouched.
1) Redact with a flattening tool, never a shape tool. 2) Check metadata — the title or author field can leak too (Kameleo's Edit Metadata clears them). 3) Keep your original in a safe place; redaction is intentionally irreversible. 4) Verify: try selecting text over the redacted area in the output.
Uploading a document to redact it is self-defeating — the unredacted version now sits on someone's server. Kameleo redacts on your device; nothing is uploaded at any point.